FastRaw(3) User Contributed Perl Documentation FastRaw(3)NAMEPDL::IO::FastRaw-- A simple, fast and convenient io format for PerlDL.
SYNOPSIS
use PDL;
use PDL::IO::FastRaw;
writefraw($pdl,"fname"); # write a raw file
$pdl2 = readfraw("fname"); # read a raw file
$pdl2 = PDL->readfraw("fname");
$pdl3 = mapfraw("fname2",{ReadOnly => 1}); # mmap a file, don't read yet
$pdl4 = maptextfraw("fname3",{...}); # map a text file into a 1-D pdl.
DESCRIPTION
This is a very simple and fast io format for PerlDL. The disk data
consists of two files, a header metadata file in ASCII and a binary
file consisting simply of consecutive bytes, shorts or whatever.
It is hoped that this will not only make for a simple PerlDL module for
saving and retrieving these files but also make it easy for other
programs to use these files.
The format of the ASCII header is simply
<typeid>
<ndims>
<dim0> <dim1> ...
The binary files are in general NOT interchangeable between different
architectures since the binary file is simply dumped from the memory
region of the piddle. This is what makes the approach efficient.
It is also possible to mmap the file which can give a large speedup in
certain situations as well as save a lot of memory by using a disk file
as virtual memory. When a file is mapped, parts of it are read only as
they are accessed in the memory (or as the kernel decides: if you are
reading the pages in order, it may well preread some for you).
Note that memory savings and copy-on-write are operating-system
dependent - see Core.xs and your operating system documentation for
exact semantics of whatever. Basically, if you write to a mmapped file
without "ReadOnly", the change will be reflected in the file
immediately. "ReadOnly" doesn't really make it impossible to write to
the piddle but maps the memory privately so the file will not be
changed when you change the piddle. Be aware though that mmapping a
40Mb file without "ReadOnly" spends no virtual memory but with
"ReadOnly" it does reserve 40Mb.
FUNCTIONS
readfraw
Read a raw format binary file
$pdl2 = readfraw("fname");
$pdl2 = PDL->readfraw("fname");
writefraw
Write a raw format binary file
writefraw($pdl,"fname");
mapfraw
Memory map a raw format binary file (see the module docs also)
$pdl3 = mapfraw("fname2",{ReadOnly => 1});
The "mapfraw" command supports the following options (not all
combinations make sense):
Dims, Datatype
If creating a new file or if you want to specify your own
header data for the file, you can give an array reference and a
scalar, respectively.
Creat Create the file. Also writes out a header for the file.
Trunc Set the file size. Automatically enabled with "Creat". NOTE:
This also clears the file to all zeroes.
ReadOnly
Disallow writing to the file.
maptextfraw
Memory map a text file (see the module docs also).
Note that this function maps the raw format so if you are using an
operating system which does strange things to e.g. line delimiters
upon reading a text file, you get the raw (binary) representation.
The file doesn't really need to be text but it is just mapped as one
large binary chunk.
This function is just a convenience wrapper which firsts "stat"s the
file and sets the dimensions and datatype.
$pdl4 = maptextfraw("fname", {options}
The options other than Dims, Datatype of "mapfraw" are supported.
BUGS
Should be documented better. "writefraw" and "readfraw" should also
have options (the author nowadays only uses "mapfraw" ;)
AUTHOR
Copyright (C) Tuomas J. Lukka 1997. All rights reserved. There is no
warranty. You are allowed to redistribute this software / documentation
under certain conditions. For details, see the file COPYING in the PDL
distribution. If this file is separated from the PDL distribution, the
copyright notice should be included in the file.
perl v5.10.0 2000-03-15 FastRaw(3)
